Studies on the role of the cell surface in the control of DNA replication in embryonic neural cells, using lectins and other molecular probes of cell surfaces. Characterization of tissue specific cell aggregating factors and analysis of their mode of action. The role of the cell surface in the control of glutamine synthetase induction in embryonic neural retina cells. The role of poly-A in the induction of glutamine synthetase. Changes in chromosomal proteins during differentiation of neural retina. Ontogeny and role of steroid receptors in embryonic brain and neural retina cells.